It has become increasingly desirable and, in some situations necessary, to filter air streams such as air streams which provide "cabin air" for vehicular passenger compartments. This is because vehicles tend to operate in environments which are frequently heavily polluted by emissions from other vehicles traveling on the same roadway, which emissions include a host of injurious gases, vapors and particles. This is not only the case for urban roads, but also for rural roads where pollen and dust are frequently drawn onto roadways by moving vehicles and then pulled into passenger compartments.
Filtering inlet air for vehicular cabins is a relatively new practice in which the technology is now developing and thus, there is a need for concepts which are of particular interest with respect to this technology. The concepts developed to improve the quality of cabin air also may have application for treating air streams in general and specifically, for cleaning combustion air prior to the air entering an internal combustion engine.